The invention relates to a method and arrangement for supplying a maximum quantity of fuel to a combustion engine.
It is known to develop fuel injection systems including carburetors, electrically controlled carburetors, electric and mechanical fuel injectors and like systems, in such a manner that, depending on the actual operational altitude of the combustion engine above sea level, a so-called altitude correction is provided in order to correct the respectively injected amount of fuel to the combustion engine to the decreasing air density for maintaining the predetermined mixture proportions of the fuel-air mixture. Consequently, the higher the operational altitude of the combustion engine above sea level, the lower is the amount of fuel that has to be injected. Through such a provision it is prevented that a motor vehicle driving in different elevations, for example driving from a valley to higher elevations, is supplied with an increasingly rich mixture which leads to an increase of consumption and leads to problems concerning environmental protection.
In fuel injectors, so-called air volume measuring systems (air meters) are used for determining the amount of air actually supplied to the combustion engine. These air meters render necessary a correction of the amount of injection in response to decreasing air density. It is common to subject the output signal of the air meter to a preferably continuously working correction divided from an altimeter which can also be developed as an elevation sensing switch. The determined correction is based on the deviation of the measured air meter signal with respect to a theoretical value. In this case, the measured air meter signal corresponds to the theoretical value with a tolerance of about 5% per 1000 m.
In each combustion engine there are, however, operating conditions in which the supplied amount of fuel is not determined by the otherwise considered operating parameters of the combustion engine but are determined by a maximum critical value which should not be exceeded. With regard to fuel injectors, for example if electric fuel injectors are employed, this means that a separate circuit generates injection impulses of maximum duration in addition to and synchronously with the fuel injecting impulses calculated under regular conditions. The injection impulses as well as the impulses of maximum duration are combined in a gate circuit and are transmitted to a succeeding multiplication stage. This maximum impulse time limitation, i.e. the maximum amount of fuel supplied under special operating conditions to the combustion engine by the fuel injection system, is a constant value which under normal operating conditions to which also a standard operational elevation or altitude belongs has proven to be an optimum value with respect to the exhaust gas and driving quality.
The prior art system, however, has the disadvantage that the maximum value of the injected fuel amount is constant regardless of the operational altitude of the motor vehicle. Upon operation in high elevations, this leads to a too rich fuel injection and consequently to an excessively rich fuel-air mixture.